Electric alarm clock control



May 9, 1950 oss 2,507,216

ELECTRIC ALARM CLOCK CONTROL Filed Jan. 2, 1945 INVENTOR B 111%, M M Lddtzw Patented May 9, 1950 ELECTRIC ALARM CLOCK CONTROL Eric Beecroft Moss, Cricklewood, London, England, assignor to S. Smith & Sons (England), Limited, London, England, a company of Great Britain Application January 2, 1945, Serial No. 571,092 In Great Britain October 28, 1943 2 Claims. 1

This invention relates to electric buzzers, and particularly to buzzers employed in electric clocks, and of the kind comprising a vibratory element energised by an electro-magnet and means for silencing the buzzer. It is usual to silence such buzzers either by interrupting the current supply to the electro-magnet or by pressing the vibratory element into engagement with the pole face, or faces, of the magnet. It is not always convenient, however, to interrupt the supply, and if the buzzer is to be silenced by pressing the vibratory element against the pole face, or faces, considerable force is necessary to ensure that no air gap is left which might result in some vibration, and therefore some noise. This is particularly the case when the electro-magnet is energized by an alternating supply.

One of the objects of the present invention is to provide improved means for silencing a buzzer, while another object is to provide a construction in which secondary noises in the buzzer are avoided.

According to this invention, an electric buzzer of the kind referred to above is characterised in that the silencing means comprise a movable control member arranged to constrain the vibratory element against movement towards the pole face, or pole faces, of the electro-magnet when the buzzer is required to be silenced. It is found with such an arrangement that very little force is required to operate said control means, and therefore the device is particularly applicable to electric clocks in which the control means is operated by a moving part of the clock. Preferably, the control member is movable into engagement with that side of the vibratory element, or with a part attached thereto, which is adjacent to the pole face, or faces.

In order to eliminate any tendency for the vibratory element to vibrate against the aforesaid movable member, one or other of these parts may be in itself resilient. For example, the control member may comprise a lever arm which is arranged to engage the free end of a leafspring anchored at the other end to the vibratory element.

In applying the invention to an electric alarm clock the control means for constraining the vibratory element against movement towards the electro-magnet is actuated by a cam, or the like, driven by the clock mechanism.

According to another feature of the invention the aforesaid vibratory element may be pivotally mounted so as to be capable of swinging bodily towards and away from the electro-magnet, and

is provided with an armature arranged opposite a pole face or pole faces of the magnet, and a st p is arranged in the path of pivotal movement part of the vibratory element so as to space he armature at one limit of its movement a ho-rt distance from said pole face, or faces, at cast a part of which vibratory element between he stop and armature is resilient, and yielding means are provided for urging the vibratory element against said stop.

With this arrangement, when the vibratory element is brought into engagement with the stop the element vibrates about the stop which forms a fulcrum point. Preferably, the resilience is so chosen that the natural period of vibration of the vibratory element is the same as the frequency of the alternating supply for the electro-magnet.

The aforesaid stop may be adjustable so as to vary the minimum distance between the armature and pole face, or faces.

The above arrangement is particularly applicable to the case where the vibratory element is mounted to swing bodily about a pivot axis, and in one constructional form of the invention the vibratory element comprises two arms extending from and connected together near the axis of pivoting, one of which arms is arranged to cooperate with said stop, and the other of which carries or is formed with said armature. The former arm may be resilient and the latter arm may be comparatively rigid. The aforesaid means for urging the vibratory element towards said stop may comprise a helical spring encircling a pivot shaft on which the two arms are pivotally mounted, one end of which spring engages the rigid arm and the other a fixed part of the apparatus.

The following is a brief description of the invention as applied to a twenty-four hour electric alarm clock, reference being made to the accompanying drawing which is a diagrammatic side elevation of the buzzer mechanism.

The clock movement is driven by a synchronous electric motor connected in series with the energising coil ID of an electro-magnetic buzzer. The electro-magnet comprises a U-shaped core I I arranged with its limbs in a horizontal plane and the pole faces l2 vertical. The armature I3 is formed at the lower end of a lever arm 14 which is provided at its upper end with a hub portion l5 encircling a pivot shaft 15. Both the electromagnet and the pivot shaft are secured between two plates I! (one of which is not shown) in which the various spindles of the clock movement are mounted. The aforesaid hub portion did of the lever arm has integrally secured to it a second lever arm l8 of lesser width and the resilience of which is so chosen that the natural period of vibration of the system l4, l8, I9 is the same as the frequency of the electric supply for the electro-magnet, e. g'., 50 cycles per second. This lever arm is arranged to stop short of the end of the other arm which is T-shaped to provide the aforesaid armature. Secured to the face of this second arm on the same side as the electromagnet is a leaf-spring 19 which is anchored to the arm adjacent the aforesaid hub, the natural periodicity of the leaf-spring being chosen so as to be different from that of the system l4, l8, l9. The vibratory element thus formed is capable of being swung bodily towards and away from the electro-magnet, and its inward movement is limited by a stop 20 carried by one of the aforesaid plates, which stop is formed by an eccentric which may be adjustably rotated so that when the second arm comes into contact therewith the spacing of the armature on the other arm may be regulated with respect to the electro-magnet for the purpose of adjusting the loudness of the alarm. The vibratory element is urged towards this position by a helical spring 2! which encircles the shaft and has one end 22 which engages a part of the vibratory element and the other end 23 which engages one of said mounting plates. The vibratory element may be swung out of the influence of the electro-magnet b means of a bell-crank lever 24 pivoted between the aforesaid plates and having one arm 25 thereof arranged to engage the aforesaid leaf-spring I9. The bell crank 24 is adapted to be moved about its pivot by a cam-disc 21 adjustably rotatable with respect to the twenty-four hour wheel. For this purpose, a projection 28 on the first said arm 25 of the bell-crank lever is arranged to engage the periphery of the cam-disc and drop into a recess 29 therein at a preset time. The aforesaid bell-crank lever is provided with a manipulating knob 30 by which the armature may be moved clear of the influence of the electro-magnet, and a detent 31 is provided for engaging an abutment 32 on the bell-crank lever arm 26 whereof the armature is held in the retracted position, which detent is arranged to be tripped by a pin 33 on the aforesaid cam disc at an appropriate time.

Thus, although the buzzer ma be stopped by 50 hand after it has been set into operation by the clock mechanism the detent will be automatically released after the recess 29 is no longer opposite the projection 28 and the armature is retained at a distance away from the magnet.

Iclaim:

1. An electric buzzer for an electric clock in which the buzzer is controlled by a cam driven by the movement of the clock, which buzzer comprises a vibratory element, an electromagnet adapted to vibrate said element, a pivotally mounted bell-crank lever, vibration-absorbing means interposed between one arm of said bellcrank lever and the vibratory element, a manipulating element on the other arm of the bell-crank lever, said bell-crank lever being adapted to engage with said cam and move the vibratory element into a position away from the said electromagnet, a detent for holding said bell-crank lever when moved by said manipulator into the said position, a further member operatively connected to said cam and arranged to engage said detent, said further member being so shaped as to release said bell-crank lever from said detent at a predetermined point in the revolution of the said cam.

'2. An electric buzzer as claimed in claim 1 in which the said vibration-absorbing means are constituted by a resilient member such as a spring, and the resilience of the said member is such as to tend to maintain said bell-crank lever in engagement with said detent.

ERIC BEECROFT MOSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

